Radio transmitting apparatus, radio receiving apparatus and method therefor

ABSTRACT

By assigning a plurality of subcarriers  31  to a data channel  33  and assigning fewer subcarriers  32  than the plurality of subcarriers  31  to a control channel  34,  and in addition locating the control channel  34  at the center frequency fc of a frequency band used to transmit the data channel  33,  on the radio receiving apparatus side, the frequencies of a local signal by which the received signal is multiplied share the same value, thereby speeding up the switching between the control channel and the data channel.

TECHNICAL FIELD

The present invention relates to a radio transmitting apparatus and aradio receiving apparatus used in a digital radio communications system,and a method for them.

BACKGROUND ART

In a typical digital radio communications system using a multicarriercommunication scheme, for when communicating using a data channel fortransmitting voice data and/or image data and a control channel forcontrolling a communication station at another end and a communicationstate, a method where a small number of subcarriers are assigned to thecontrol channel while multiple subcarriers are assigned to the datachannel in order to minimized power consumption in a mobile station hasbeen proposed (Laid-Open Japanese Patent Publication No. 2001-274767,Laid-Open Japanese Patent Publication No. 2001-285927).

In this method, a receiving apparatus performs A/D conversion on thecontrol channel at a relatively low sampling rate in order to receivethe control channel of narrowband comprising a small number ofsubcarriers, and in response to having received the control channel, thesampling rate of A/D conversion for the received signal is taken to behigh to prepare for receiving the data channel of wideband comprisingmultiple subcarriers.

However, in this conventional receiving apparatus, because the centerfrequency of a data channel comprising a plurality of subcarriers 2 isdifferent from the center frequency of a control channel 6 as shown inFIG. 1, the frequency of a local signal for down-converting thesubcarriers of the control channel 6 needs to be changed in order toswitch from the receiving of the control channel 6 to that of the datachannel 4 as shown in FIG. 2.

Here, the local signal is a signal whose frequency is set to the centerfrequency of a transmit frequency band on the transmitter side and bywhich a D/A-converted, transmitting signal is multiplied to up-convertthe transmitting signal. On the receiver side, the signal received viaan antenna is multiplied by a local signal to down-convert the receivedsignal.

Therefore, when the center frequency of the control channel 6 isdifferent from the center frequency of the subcarriers of the datachannel 4, the local signal's frequency needs to be changed to thecenter frequency of the data channel 4 after receiving the controlchannel 6, in order to receive the data channel 4. Until a PLL (PhasedLocked Loop) circuit generating the local signal becomes stable inchanging the local signal's frequency, it is difficult to switch fromthe receiving of the control channel 6 to that of the data channel 4,thus having prevented the speeding up of switching between the controlchannel 6 and the data channel 4.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a radio transmittingapparatus and a radio receiving apparatus that can switch between thecontrol channel and the data channel at high speed on the radioreceiving apparatus side, and a method therefor.

In order to achieve the above object, according to the presentinvention, a plurality of subcarriers are assigned to a data channel,and fewer subcarriers than the plurality of subcarriers are assigned toa control channel, and, in addition, the control channel is located atthe center frequency of a frequency band used to transmit the datachannel, so that, on the radio receiving apparatus side, the frequenciesof a local signal by which the received signal is multiplied share thesame value. Thus, switching between the control channel and the datachannel can be speeded up.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a signal waveform for explaining a conventionaloperation;

FIG. 2 is a schematic view for explaining the conventional operation;

FIG. 3 is a block diagram showing the configuration of a radiotransmitting apparatus according to embodiment 1 of the presentinvention;

FIG. 4 is a view of a signal waveform showing a transmitted signalaccording to the embodiment 1;

FIG. 5 is a block diagram showing the configuration of a radio receivingapparatus according to the embodiment 1 of the present invention;

FIG. 6 is a schematic view for explaining an operation of the embodiment1 of the present invention;

FIG. 7 is a block diagram showing the configuration of a radiotransmitting apparatus according to embodiment 2 of the presentinvention;

FIG. 8A is a schematic view for explaining an operation of theembodiment 2 of the present invention;

FIG. 8B is a schematic view for explaining an operation of theembodiment 2 of the present invention;

FIG. 9 is a block diagram showing the configuration of a radio receivingapparatus according to the embodiment 2 of the present invention;

FIG. 10 is a view showing a signal waveform for explaining anotherembodiment;

FIG. 11A is a view showing a signal waveform for explaining anotherembodiment;

FIG. 11B is a view showing a signal waveform for explaining anotherembodiment;

FIG. 12 is a view showing a signal waveform for explaining anotherembodiment; and

FIG. 13 is a view showing a signal waveform for explaining anotherembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the drawings.

Embodiment 1

FIG. 3 is a block diagram showing the configuration of a radiotransmitting apparatus 10 according to embodiment 1 of the presentinvention. In FIG. 3, the radio transmitting apparatus 10 is provided ina base station apparatus or a mobile station apparatus, and is formultiplexing a control channel signal and a data channel signal totransmit. In this embodiment, a case will be described where a signal istransmitted using a bandwidth of 100 MHz in a frequency band with itscenter frequency being 5 GHz.

In the radio transmitting apparatus 10, a bandwidth of 1 MHz is used forthe control channel, and a bandwidth of 99 MHz, which is not used forthe control channel, is used for the data channel of the bandwidth of100 MHz.

The control channel signal is spread in a spreading section 11 andmodulated according to a predetermined modulation scheme in a modulationsection 12, and then supplied to a multiplexing section 14. Furthermore,the data channel signal is modulated in a modulation section 13, andthen supplied to the multiplexing section 14. The multiplexing section14 multiplexes the control channel signal and the data channel signalsuch that the control channel signal is mapped to the center frequencyof a transmit band with respect to the modulated control channel signaland data channel signal.

The output of the multiplexing section 14 is supplied to aserial-parallel conversion section (S/P) 15 to be serial-parallelconverted, and then inverse-fast-Fourier transformed in an IFFT (InverseFast Fourier Transform) section 16. As a result of theinverse-fast-Fourier transforming, the bandwidth becomes 100 MHz.

The output of the IFFT section 16 is converted into an analog signal ina digital-analog (D/A) conversion section 17, and then multiplied by alocal signal (carrier signal) in a multiply section 18. Because thefrequency of the local signal is set at the center frequency (5 GHz) ofthe band in use for transmitting, a signal obtained by multiplying bythe local signal in the multiply section 18 has been up-converted to thetransmit band (5 GHz±50 MHz). After being amplified in an amplifier(AMP) 19, the signal is transmitted via an antenna 21.

A multicarrier signal generated in the radio transmitting apparatus 10in this manner is so structured that, as shown in FIG. 4, the number ofsubcarriers 32 composing the control channel 34 is less than the numberof subcarriers 31 composing the data channel 33, and is in a state wherethe control channel 34 is located at the center frequency fc of thetransmit band (FFT range) of the data channel 33.

By locating the control channel 34 at the center frequency fc of thedata channel 33 as described above, a common local frequency can be usedon a receiving apparatus side described below when down-converting.

FIG. 5 is a block diagram showing the configuration of a radio receivingapparatus 40 provided in a mobile station apparatus or a base stationapparatus. In FIG. 5, the transmitted signal from the radio transmittingapparatus 10 received via an antenna 41 is amplified in an amplifier 42,and then supplied to a multiply section 43. The multiply section 43performs mixing by multiplying the signal supplied from the amplifier 42by a local signal set at 5 GHz, i.e. the signal's center frequency. As aresult, the signal input into the multiply section 43 is down-converted.

A channel selecting section 46 allows only the control channel 34 of thereceived signal to pass through by controlling a band-pass filter 44 tohave the band of 1 MHz pass to match the control channel 34 of thereceived signal. In this case, the channel selecting section 46 controlsan analog-digital (A/D) conversion section 45 to sample the controlchannel 34 at a sampling rate of 1 Msps to match the bandwidth of thecontrol channel 34.

Moreover, the channel selecting section 46 allows the data channel 33contained in the received signal to pass through by controlling theband-pass filter 44 to have the band of 100 MHz pass to match the datachannel 33 of the received signal. In this case, the channel selectingsection 46 controls the analog-digital (A/D) conversion section 45 tosample the data channel 33 at a sampling rate of 100 Msps to match thebandwidth of the data channel 33.

A switch section 47, when selecting the data channel 33, supplies thesignal of the data channel 33 to an FFT (Fast Fourier Transform) section48 by being switched to a first switch output port side. After beingfast-Fourier transformed, the signal of the data channel 33 supplied tothe FFT section 48 is supplied to a parallel-serial (P/S) section 49,and after being converted into a serial signal, is demodulated in ademodulation section 51.

On the other hand, the switch section 47, when selecting the controlchannel 34, supplies the signal of the control channel 34 to ademodulation section 50 by being switched to a second switch output portside. The signal of the control channel 34 demodulated in thedemodulation section 50 is then despread in a despreading section 52.

In this manner, the multicarrier signal transmitted from the radiotransmitting apparatus 10 (FIG. 3) is received by the radio receivingapparatus 40 (FIG. 5), and the control channel 34 located at the centerfrequency fc of transmit band (the data channel 33) and the data channel33 are down-converted with the common local frequency.

As described above, by down-converting the control channel 34 and thedata channel 33 with the common local frequency, as shown in FIG. 6, thelocal frequency does not need to be changed when switching between thereceiving of the control channel 34 and the receiving of the datachannel 33. Since the local frequency does not need to be changed,switching from the control channel 34 to the data channel 33 inreceiving can be speeded up. Moreover, by dealing with the controlchannel 34 and the data channel 33 by changing the sampling rate of oneanalog-digital conversion section 45, the circuit configuration can befurther reduced compared with the case of providing respectiveanalog-digital conversion sections for the control channel 34 and thedata channel 33.

Furthermore, because the radio transmitting apparatus 10 spreads thesignal of the control channel 34 and then transmits, a receiver canextract the signal for the receiver even when using the same frequencywith a radio transmitting apparatus in the neighborhood.

Yet further, while an effect of DC (Direct Current) offset occurs on thecenter frequency of the transmit band, in the present embodiment theeffect of DC offset can be removed by spreading the control channel 34located at the center frequency, and by this means the data of thecontrol channel 34 can be received with good quality in the radioreceiving apparatus 40.

Moreover, by using only one subcarrier 32 as the control channel 34 inthe radio transmitting apparatus 10 and the radio receiving apparatus40, a filter can be designed for the radio receiving apparatus 40without taking into account interference between subcarriers, therebysimplifying the circuit configuration of the filter.

Embodiment 2

FIG. 7 is a block diagram showing the configuration of a radiotransmitting apparatus 60 according to embodiment 2 of the presentinvention. In FIG. 7, the radio transmitting apparatus 60 is provided ina base station apparatus or a mobile station apparatus, and is formultiplexing and transmitting a signal (MCS signal) notifyinginformation denoting modulation and coding schemes in packettransmission (hereinafter called MCS (Modulation and Coding Schemes)information) as a control channel, with packet data. In this embodiment,a case will be described where a signal is transmitted using a bandwidthof 100 MHz in a frequency band with its center frequency being 5 GHz.

In the radio transmitting apparatus 60, a bandwidth of 1 MHz is used forthe MCS signal, and a bandwidth of 99 MHz, which is not used for thetransmission of the MCS signal, is used for the packet data of thebandwidth of 100 MHz.

The MCS signal is spread in a spreading section 61 and modulatedaccording to a predetermined modulation scheme in a modulation section63, and then supplied to a multiplexing section 65. Furthermore, at thesame time the data channel signal is encoded in an encoding section 62,and supplied as packet data to a modulation section 64. After beingmodulated in the modulation section 64, the packet data is supplied tothe multiplexing section 65.

The multiplexing section 65 multiplexes the MCS signal and the packetdata such that the MCS signal is mapped to the center frequency of atransmit band with respect to the modulated MCS signal and the packetdata.

The output of the multiplexing section 65 is supplied to aserial-parallel conversion section (S/P) 66 to be serial-parallelconverted, and then inverse-fast-Fourier transformed in an IFFT (InverseFast Fourier Transform) section 67. As a result of theinverse-fast-Fourier transforming, the bandwidth becomes 100 MHz.

The output of the IFFT section 67 is converted into an analog signal ina digital-analog (D/A) conversion section 68, and then multiplied by alocal signal (carrier signal) in a multiply section 69. Because thefrequency of the local signal is set at the center frequency (5 GHz) ofthe band in use for transmitting, a signal obtained by multiplying bythe local signal in the multiply section 69 has been up-converted to thetransmit band (5 GHz±50 MHz). After being amplified in an amplifier(AMP) 70, the signal is transmitted via an antenna 71.

Of a multicarrier signal generated in the radio transmitting apparatus60 in this manner, the packet data 95, in which the MCS signal 96, whichis the control channel signal, is located at the center frequency, istransmitted subsequently to the MCS signal 96 as shown in FIG. 8A.

By locating the MCS signal 96 at the center frequency of the packet data95 as above, a common local frequency can be used on a receivingapparatus side described below when down-converting.

FIG. 9 is a block diagram showing the configuration of a radio receivingapparatus 80 provided in a mobile station apparatus or a base stationapparatus. In FIG. 9, the transmitted signal from the radio transmittingapparatus 60 received via an antenna 81 is amplified in an amplifier 82,and then supplied to a multiply section 94. The multiply section 94performs mixing by multiplying the signal supplied from the amplifier 82by a local signal set at 5 GHz, i.e. the signal's center frequency. As aresult, the signal input into the multiply section 94 is down-converted.

A channel selecting section 85, in a usual state, enables only the MCSsignal 96 of the received signal to be received by controlling aband-pass filter 83 to have the band of 1 MHz pass to match the MCSsignal 96 of the received signal, with monitoring the MCS signal. Inthis case, the channel selecting section 85 controls an analog-digital(A/D) conversion section 84 to sample the MCS signal 96 at a samplingrate of 1 Msps to match the bandwidth of the MCS signal 96.

Then, when the MCS signal 96 is received, the MCS signal 96 is suppliedvia a switch section 86 to a demodulation section 88. After beingdemodulated in this section, the MCS signal 96 is despread in adespreading section 90 and supplied to an MCS interpreting section 93.The MCS signal 96 includes information about whether packet data for theradio receiving apparatus 80 is transmitted in the next slot andinformation about its modulation scheme and coding rate. The MCSinterpreting section 93 interprets this information contained in the MCSsignal 96, and supplies information for controlling the bandwidth of theband-pass filter 83 to select packet data and information forcontrolling the sampling rate of the analog-digital conversion section84 to select packet data to the channel selecting section 85, and at thesame time, supplies information denoting the demodulation scheme readout from the MCS signal 96 to a demodulation section 91, whichdemodulates packet data, and also information denoting the coding rateread out from the MCS signal 96 to an error correction section 92.Thereby, it becomes possible that in response to incoming packet data,the band-pass filter 83 and the analog-digital conversion section 84performs band-pass and conversion-into-digital processing, that thedemodulation section 91 demodulates according to the specified scheme,and that the error correction section 92 performs error correction,controlling the coding rate specified by the MCS information.

For example, when packet data is expected to be received in the nextslot from interpreting the MCS signal 96, by controlling the band-passfilter 83 to have the bandwidth of 100 MHz pass to match the packet data95, the packet data 95 contained in the received signal is allowed topass through. In this case, the channel selecting section 85 controlsthe analog-digital (A/D) conversion section 84 to sample the packet data95 at a sampling rate of 100 Msps to match the bandwidth of the packetdata 95.

Moreover, the switch section 86, when the received signal is the packetdata 95, supplies this received signal to an FFT (Fast FourierTransform) section 87 by switching its switch output ports according toa schedule to receive the packet data 95 interpreted in the MCSinterpreting section 93. After being fast-Fourier transformed, thepacket data 95 supplied to the FFT section 87 is supplied to aparallel-serial (P/S) section 89 and converted into a serial signal, andthen demodulated in the demodulation section 91. For this demodulation,the demodulation scheme is determined based on information interpretedfrom the MCS signal 96.

Then, the error correction section 92 performs error correction on thepacket data 95 demodulated in the demodulation section 91. In this errorcorrection, the packet data is finally extracted controlling the codingrate based on information interpreted from the MCS signal 96 in the MCSinterpreting section 93.

In this way, interpreting the MCS information contained in the MCSsignal 96 by the MCS interpreting section 93 enables adaptive receivingprocessing in accordance with the receive schedule and the modulationscheme and the like of the packet data 95 received after the MCS signal96.

Accordingly, in a usual state, the radio receiving apparatus 80 needonly monitor whether or not the MCS signal 96 has been received, in astate where only the MCS signal 96 with a narrowband can be received.Thus the sampling rate of the analog-digital conversion section 84 canbe reduced, and thereby power consumption can be reduced. As can be seenfrom FIG. 8B showing the case where the bandwidth of an MCS signal 102transmitted before packet data 101 is equivalent to that of the packetdata 101, the sampling rate of the analog-digital conversion section ofthe radio receiving apparatus can be reduced by an amount correspondingto the bandwidth of the MCS signal 102 being wide.

Furthermore, by transmitting the modulation scheme and the coding schemeof the packet data 95 being contained in the MCS signal 96, thisinformation can be notified to the radio receiving apparatus 80 onlyjust before the packet data 96 is transmitted, thus the powerconsumption of the radio receiving apparatus 80 can be reduced.

OTHER EMBODIMENTS

The above embodiments have described the case where the data channel 33and the control channel 34 are located close to each other as shown inFIG. 4, but the present invention is not limited to this. As shown inFIG. 10, guard frequency bands 111 and 112 may be provided between thecontrol channel 34 and the data channel 33 by controlling, for example,the IFFT section 16 (FIG. 3). By this means, the pass bandwidth of theband-pass filter 44 (FIG. 5) can be widened, and the circuit scale ofthe filter can be reduced.

Furthermore, the above embodiment has described the case where the guardfrequency bands 111 and 112 between the control channel 34 and the datachannel 33 are the same in width as shown in FIG. 10, but the presentinvention is not limited to this. As shown in FIG.'s 11A and 11B, guardfrequency bands 121 (131) and 122 (132) may be different in width. Bythis means, in a multi-cell environment, when a plurality of basestations as radio transmitting apparatuses transmit the control channel34 and the data channel 33 at the same time, the center frequencies fcof the transmit frequency bands of a plurality of mobile stations asradio receiving apparatuses are shifted on a per cell basis to centerfrequencies fc1, fc2 and the like, and thus, the control channel 34 isused at different frequencies between the cells (the control channels 34being configured according to FDMA (Frequency Division MultipleAccess)), while local signals of the control channel 34 and the datachannel 33 are used at the same frequency.

In the multicell environment, the arrangement of the control channel 34can be changed adaptively according to the situation of neighboringcells by changing the width of guard frequencies by controlling, forexample, the IFFT section 16, and thereby interference to the controlchannel 34 can be reduced. Here, in the case where the radiotransmitting apparatus 10 is a mobile station, the radio transmittingapparatus 10 may measure information about neighboring cells from thereceived signals and change the width of guard frequencies using themeasuring results, so that the guard frequencies can be controlled basedon actually measured information.

Furthermore, the previous embodiments have described the case where onlyone subcarrier 32 is used as the control channel 34, but the presentinvention is not limited to this. As shown in FIG. 12, for example, aplurality of subcarriers 32 may be used as the control channel. By thismeans, each mobile station that is a radio receiving apparatus canextract and receive only a necessary control channel.

Yet further, by performing Nyquist filtering on the control channel 34by a Nyquist filter 141 and transmitting as shown in FIG. 13,interference in other subcarriers (subcarriers 31 of the data channel)can be minimized, and also on the radio receiving apparatus side, byusing a Nyquist filter, it becomes possible to receive at minimizedinter-code interference, so that the receiving performance can beimproved.

Still further, by adopting a paging channel indicating that an incomingcall exists as the control channel 34, the sampling rate of theanalog-digital conversion section can be reduced on the radio receivingapparatus side when a call is not in progress, the power consumption ofthe radio receiving apparatus can be reduced.

As described above, according to the present invention, a plurality ofsubcarriers are assigned to the data channel and fewer subcarriers thanthe plurality of subcarriers are assigned to the control channel, and inaddition the control channel is located at the center frequency of thefrequency band used to transmit the data channel. Thus, on the radioreceiving apparatus side, the frequencies of the local signal by whichthe received signal is multiplied are common, and thereby switchingbetween the control channel and the data channel can be speeded up.

The present description is based on Japanese Patent Application No.2002-114870 filed on Apr. 17, 2002, entire content of which isincorporated herein by reference.

1. A radio transmitting apparatus, for transmitting an OFDM multicarriersignal comprising a first plurality of subcarriers and a secondplurality of subcarriers, said radio transmitting apparatus comprising:an assigning section operable to assign a data channel to the firstplurality of subcarriers of the multicarrier signal and to assign acontrol channel to the second plurality of subcarriers of themulticarrier signal, wherein the second plurality of subcarriers arelocated between the first plurality of subcarriers on a frequency axisand the center frequency of the data channel and the center frequency ofthe control channel are common; an up-conversion section operable toup-convert the multicarrier signal to a carrier frequency; and atransmitter operable to transmit the up-converted multicarrier signal.2. The apparatus according to claim 1, wherein the assigning sectionprovides a guard frequency band between the first plurality ofsubcarriers and the second plurality of subcarriers.
 3. A base stationapparatus equipped with said radio transmitting apparatus according toclaim
 1. 4. A mobile station apparatus equipped with said radiotransmitting apparatus according to claim
 1. 5. A method fortransmitting an OFDM multicarrier signal comprising a first plurality ofsubcarriers and a second plurality of subcarriers, said methodcomprising: (a) assigning a data channel to the first plurality ofsubcarriers and a control channel to the second plurality ofsubcarriers, wherein the second plurality of subcarriers are locatedbetween the first plurality of subcarriers on a frequency axis and thecenter frequency of the data channel and the center frequency of thecontrol channel are common; (b) up-converting the multicarrier signal toa carrier frequency; and (c) transmitting the up-converted multicarriersignal.
 6. The method according to claim 5, wherein step (a) comprisesproviding a guard frequency band between the control channel and thedata channel.